Switching system



May 14, 1935;

G. T. LORANCE SWITCHING SYS TEM Filed March 29, 1953 lNl/ENTOR By G. 7.' LORANCE ATTORNEY Patented May 14, 1935 UNITE D- 1 STATES FATE NT} orr -l ce swlronmc SYSTEM? George Ti Lorancc, Chappaqua,

to Electrical RescarchwProducts', Inc., York, N. Y., a corporation of Application March 29, 1933, Serial No. 663,282 t r w r 7 3 was. (o1. mam-a invention relates to communication s ysterns 'andpmore particul'a M to methods and anparatus for rapidly e'fiecti g switching operations such: systems a f Anobjcot of the: inventioii is to provide means:

I switching operatiom for gradually reducing the amplitude of signals in one communication channel and gradually increasing the amplitude or signals invanother communication channel where the two" channels 1 are associatedwitha common output circuit.

A denature of theinvention is that noslidirrgr contacts-are required for effecting the gradual; changes'irr signalamplitude; v i g ,1 nmothcr feature of the invention is that the oncdinitiated; proceeds as, tomaticall'y andmwlthany desired rapidity,

-llmacco-rdanca with one embodiment, ot the present invention there'is provided each of the two"; communication; channels a space dis-=- chargedeviceto oneof which is ap'pl iedr a potential-i that renders the channel in which it is in? eluded inoperative; Whenthe latter channel -Sflytfi) be substituted. for the operative one; a Switch is" manually operated which causes: the disabling potential to be gradually removed from the one discharge device and simultaneously a disabling potential tobe gradually applied to the discharge device in the other channeL Th-e invention" finds a particular application in soun d reproducing systems, where-a plurality ot'separate! sound records are to be associated succession with. the samereproducing channel without anoticeable break being occasioned by the transfer from one sound record to-another; Such'a system has been chosen v for the purpose 0il111$tf3$jillg-8k specific embodiment of the presentvi miention. v I v v L Other obj c-ts and; features of the invention as embodied the preferred; form will appear in titre followinggdctailed description and, the claimshereto annexed.

Inthe drawing, t

Fig. 1 shows schematically a sound picture systemin. which an embodiment ot the invention isincorporated; and v j 1 i Figs. to 4 show chematically forms oi photoelectric cell circuits which the invention maybeemployed. v I In the sound picture. system represented in Fig lf thereiis provided at each of' two alternativelyoperated picture projection machines a photoelectric "eel-1. circuit adapted to convert the sound traces on the respective films 2 into equivalent electrical waves These waves are trans-v ficrredoverfa pair of conductors to remotely lotransmitted to the amplifier.

Gated individual amplifiers V1 and V2, which in turn are connected to a common power amplifier V3 operating a sound reproducer' 35. -The in-- dividual amplifiers are operative only when. the corresponding projecting machine is inoperation. i l i t The two photoelectric cell circuits are identical. Polarizing-potential for each cell 3' is supplied from a negative point on avoltage dividing re sister 43 associated with an alternating current operated power supply unit, over a conductor lihthrough the lower contact of switch S1, and resistanceB- to cathode 5- of the cell. The positive side of the polarizing circuit is completed from the grounded terminalof voltage dividing resistor 43, through tubular conductor H resistor 1 and resistor B, to anode l of the cell. The anode of the cell is connected tothe central conductor #2 of a coaxial conductorcable leadingvto the remotely located amplifier tube V1, to the control grid of which it is connected through a condenser l4. Cathode 5 of the cell is connected through a condenser Hi to the outer conductonll of the coaxial cable to which the cathode of amplifier tube V1, is connected, and to; ground, t

gInfa specific reproducing systempresistors 9, l and (i were l00;0 00,. 500 and 100,000 ohms, respcctively; andthc capacity of condenser il was two microfarads. Resistor 9 and condenser ID together compri se a low frequency filter for suppressing ripples in the photoelectric cell polarizi Terminals are associated with resistor l to provide tor the alternative connection of a disc pick-up circuit, Ordinarily resistor 'l' vistshortcircuited through the upper contact of switch S1,: but when the switch is operated the short circuit'isremoved; the photoelectric cell circuit is disabled, andsignals from the disc pick-up are I;t'is to be' noted that the polarizing voltage for the cell is not transmitted over the conductor pair traversed by the signals. Microphonic noise that would otherwise be produced by relative movement of the conductors comprising the signal; pair is thereby substantially eliminated.

Whatever direct-current voltage does exist between the signaling conductorsby virtue of the voltage drop in resistors G and This small and ineffective in creating microphonic noise. The

general principle to be observed in thedesign is that points. at a high. direct-currentpotential above ground should be connected to ground through paths of low alternating-current impedance.

Alternative forms of photoelectric cell circuits embodying the foregoing principle are shown in Figs. 2 to 4. Fig. 2 shows a transformer-coupled circuit in which the positive terminal of the polarizing source B is connected through a halfmegohm resistor to the anode of the cell 3, and the grounded negative terminal is connected through the primary winding of transformer 52 to the cathode. The cathode of the cell, which is at a high positive potential above ground, is connected to ground through a'large condenser 53, a path of low alternating-current impedance. In the photoelectric cell circuits represented in Figs. 3 and 4, the cell is coupled to an associated amplifier through a resistor 54, which may be of the order of a half megohm. Cathode circuit resistor 55 and grid leak 56 were 18 ohms and megohms, respectively, in a particular instance. The signal output terminals of the circuits shown in Figs. 2 to 4 may be associated with the tubes V1, V2 through any suitable coupling circuit.

The individual amplifiers shown in Fig. 1 employ screen grid tubes V1, V2 of the multi-mu type. Grid polarizing potential is supplied to each from an individual potentiometer P1, P2 through a connection including a resistor l5, which may be of the order of 10 megohms, and a resistor 16, which may be 1 megohm. The potentiometers P1 and P2 comprise movable contacts l9 and 20, respectively, and respective resistors 2| and 22, which are connected in parallel between ground and a negative point on resistor 43. Volume control is secured by adjustment of the potentiometer contacts.

In the input circuits of each of the screen grid tubes V1, V2, there is provided between the junction of resistors l5 and I6 and the cathodes of the tubes a condenser II, which in conjunction with resistor l6 constitutes a grid biasing filter. In accordance with the embodiment of the invention herein disclosed the same filter may be used to control the rate of fade-over from one channel to another, as will now appear.

In the grid circuits of each of the tube V1, V2 there is provided a double-pole, double-throw switch S3, which in one position applies to the control grid of one tube a high negative disabling potential, and connects the control grid of the other tube to one of the potentiometer contacts I9, 20. In the alternative position of the switch, thedisabling potential is transferred to the grid of the other tube and the grid of the first tube is connected to the other potentiometer contact. The left hand contacts associated with the respective blades of switch S3 are connected together to the extreme negative terminals of the volume controlling potentiometers. When the blades of switch S3 are thrown inward, the movable contact 20 of potentiometer P2 is disconnected from the grid of tube V2 and a negative voltage, which in a particular instance was approximately '75 volts, is applied to the control grid of tube V2. With the blades of switch S3 thrown outward, a negativevoltage sufficient to render tube V1 inoperative is connected in the control grid circuit of that tube. Because of the effect of resistor l6 and condenser l1, however, this voltage does not build up immediately but in accordance with an exponential curve. As a result of this gradual increase in negative grid bias the volume of signals in the upper channel is reduced gradually, finally becoming substantially zero.

While the upper reproducing channel is operative a disabling negative potential is normally applied to the control grid of tube V2 in the other reproducing channel as described above. When a changeover is to be made, switch S3 is thrown to its alternative position, the high voltage source is thereby disconnected from the grid circuit of tube V2, and the negative potential on that grid is gradually dissipated through resistors l5 and IS, the rate of dissipation being determined by the relative magnitudes of resistor l6 and condenser l1. At some point during this gradual decrease in grid bias on tube V2, that tube begins to become operative and the volume of signals gradually increases up to normal volume.

Thus, by operation of switch 53, the volume of signals in one channel may be caused to gradually approach zero and at any desired point the volume of signals in the other channel to be gradually increased. The transfer from one channel to the other therefore takes place smoothly and gradually and without any manual control other than the initial operation of switch S3.

The anodes of tubes V1 and V2 are connected together and through condenser 25 and inductance 26 in series to the grid of the common amplifier tube V2. Anode current is supplied to the first two tubes through an inductance 40 connected to a point of positive potential on the voltage divider 43. Inductance 26 is so proportioned with respect to the inherent capacity between the grid of tube V3 and ground as to be resonant at the high frequency end of the transmission band to maintain the high frequency gain. Inductance 40 and condenser 25 are so proportioned as to approximate a half section of a high-pass filter with a cut-off frequency of roughly 25 cycles per second and having an impedance approximating that of the terminating resistance connected across the grid circuit of the succeeding tube. An improvement in the gain at low frequencies is thereby obtained.

The anode of tube V3 is connected to the power supply unit through resistance 30 and to the grid of the succeeding pentode amplifier stage V4 through condenser 3| and inductance 33. The latter inductance functions in the same manner and for the same purpose as inductance 26 associated with tube V3. The output signal of tube V; is transmitted through transformer 34 to sound reproducer 35.

While for purposes of exposition the present invention has been shown and described as embodied in a specific form and in cooperation with a'sound picture reproducing system, it is capable of numerous other forms of embodiment and uses within the scope and spirit of the appended claims.

What is claimed is:

1. In a sound picture reproducing system, two sound reproducing channels, each of said channels including a photoelectric cell and a space discharge amplifying device having a control electrode that is connected to said cell through a circuit of high impedance, an output circuit com-,

mon to said channels, a filter comprising resistance and capacitance in the biasing circuit connected with each of said control electrodes, and means for applying a disabling potential alternatively to said control electrodes through said respective associated filters, whereby upon the operation of said means the amplitude of signals gradually decreases in one of said channels and gradually increases in the other without a noticeable interruption of signals in said output circuit.

2. A pair of individual signal transmission channels to be selectively associated in energy transfer relation with a common output circuit, asignal repeating space discharge device in each of said channels, each of said devices having an impedance controlling electrode, independent filters connected to said respective electrodes, and means for applying a disabling potential alternatively to said electrodes through said respective filters, whereby upon the operation of said means the amplitude of signals gradually decreases in one of said channels and gradually increases in the other without occasioning a noticeable interruption of signals in said output circuit.

3. A sound reproducing system comprising two alternatively-operative signal channels, a com-v mon output circuit for said channels, a space discharge amplifier in each of said channels, each of said amplifiers having a control electrode, independent filters connected to said control electrodes, a source of direct voltage, volumecontrol means for applying to said respective control electrodes through said respective filters an adjustable voltage derived from said source, and other means for applying alternatively to said electrodes through said respective filters a voltage derived from said source sufficient to block transmissionthrough the corresponding channel, the constants of said filters being proportioned so that upon operation of said other means the gain of one of said amplifiers gradually increases and that of the other simultaneously gradually de: creases.

GEORGE T. LORANCE. 

